Microelectromechanical (MEMS) devices have found many applications in basic signal transductions. For example, MEMS-based spatial light modulators are transducers that modulate incident light in a spatial pattern in response to optical or electrical inputs. The incident light may be modulated in phase, intensity, polarization, or direction. This modulation may be accomplished through the use of a variety of materials exhibiting magneto-optic, electro-optic, or elastic properties. Such spatial light modulators have many applications, including optical information processing, display systems, and electrostatic printing.
A microelectromechanical device often contains one or more deformable and/or deflectable members. For example, a typical micromirror-based spatial light modulator consists of an array of deflectable mirror plates that are formed on a substrate with each mirror plate being attached to a deformable hinge. In operation, the mirror plates are individually addressable and deflectable with electrostatic fields so as to modulate incident light. The performance of the spatial light modulator depends upon the coordination of the mirror plates. That is, the successful light modulation depends on the uniformity of the mirror plates and hinges.
For quality assurance purposes, it is certainly required to inspect the functional members of microelectromechanical devices before delivery to customers. The inspection, however, is often preferably to be performed during the fabrication process for many reasons. For example, after completion of the deformable and/or deflectable elements, one or more succeeding processing steps, such as surface treatment, assembly and packaging are often required before the completion of the fabrication process. From at least the cost-effective point of view, inspection of the formed deflectable and/or deformable elements is desired to be conducted before performing the succeeding processing steps. According to the inspection, the fabricated devices not satisfying the predetermined criterion can be discarded, while the fabricated devices satisfying the criterion are saved for further processes.
Therefore, what is desired is a method and apparatus for inspecting fabricated microelectromechanical devices having deflectable and/or deformable members.